1. Field of the Invention
This invention relates to laminated cores for dynamoelectric machines or magnetic pickup or recording heads which are formed by stacking thin sheet metal core pieces each having a predetermined configuration and by welding the stacked core pieces together by means of laser beams, and a method of making the same.
2. Description of the Prior Art
In cores used for dynamoelectric machines such as electric motors or magnetic pickup or recording heads used in tape recorders, thin sheet core pieces each having a predetermined configuration are conventionally blanked out of a material and are then stacked one upon another. The stacked core pieces are combined together by welding boundaries therebetween by means of continuous or spot irradiation of laser beams.
In a prior art method, the above-described stacking of core pieces and the laser beam welding of the boundaries are executed in one continuous step. More specifically, a first core piece is blanked out of a material, and a second core piece is blanked out of the material and is stacked on the first core piece. A third core piece is then blanked out of the material and is stacked on the second core piece. The above-described sequence is repeated. Simultaneously with the above-described step, laser beams are emitted from a plurality of laser beam emitting sections disposed around the boundaries of core pieces so that the laser beams are irradiated onto a plurality of portions of circumferential edges of the stacked core pieces, thereby sequentially welding the core pieces together.
In the above-described method, the stacked core pieces include those for a plurality of core units 101 but not for a single core unit 101 as shown in FIG. 20. When irradiation of laser beams is indifferently continued under the circumstances, the stacked core pieces composing a plurality of core units 101 are welded together to be integrated. To obviate this drawback, the prior art has provided a welding manner in which laser beam irradiation is interrupted for boundary core pieces between those composing the core units 101 so that the individual core units 101 can be separated.
Unwelded portions of the core piece resulting from interruption of laser beam irradiation need to be located so as to conform to the stack thickness of the core unit 101 so that the individual core units can reliably be separated. However, the stacked core pieces are displaced in the direction of stack when the thickness of the core piece is varied. Consequently, the unwelded portions of the core piece do not conform to the timing for interruption of laser beam irradiation, that is, the unwelded portions are displaced. In such a case, the unwelded portions of the core piece are unavoidably welded such that the core units is rendered inseparable.
To solve the above-described problem, the prior art has provided installation of a thickness measuring device for measuring the thickness of each core piece for determination of a laser beam irradiation position. However, this has resulted in an increase in the cost of equipment.